1. Field of the Invention
The invention relates to automated assembly equipment particularly with respect to the vacuum grippers utilized therein for picking up components.
2. Description of the Prior Art
Vacuum grippers are utilized in present day automated assembly equipment for picking up component parts and moving the parts, for example, horizontally from one location to another. For example in automated equipment for assembling printed circuit boards, leaded components may be fed down a chute into a presentation site wherefrom they are removed by a vacuum gripper to a different location in the assembly equipment. The conventional vacuum gripper comprises a member connected to a vacuum source through a valve. The gripper is moved vertically to contact the device to be lifted and is opened to vacuum to grip the device. Equipment is included to then lift the gripper with the device secured thereto so that the pins of the component clear the walls of the presentation site. The gripper with the part affixed thereto may then be transported horizontally to another location. If the component part is not securely held on the gripper by the vacuum, the part may be dislodged when the gripper is accelerated horizontally during the transport portion of the operation. Expensive components such as pin grid arrays may be damaged if this occurs. Thus prior art vacuum grippers have a safety disadvantage because misalignment of the device with respect to the gripper or superfluous substances such as dirt or the like may prevent an adequate seal between the gripper and the part resulting in dislodgement and damage.
Prior art vacuum grippers may utilize an expensive pressure sensor that monitors the vacuum within the gripper to determine when to perform the lifting operation. When the vacuum is high enough the pressure sensor provides a signal to the motion device to lift the gripper since high vacuum within the gripper indicates a securely held part. The lifting device associated with the gripper may comprise expensive controls and secondary valving to effect the lifting operation.
Alternatively, the prior art may utilize a timer to determine when to lift the gripper. A predetermined time interval is required to exhaust the gripper and tubulation so that the component part to be picked up will be securely fastened on the gripper. The timer utilized in the prior art actuates the vertical motion device after the predetermined time interval has elapsed. Although the timer alternative is less expensive then the pressure sensor it may not be as safe since the gripper could be lifted and transported horizontally with an inadequately gripped component part.
It is appreciated, therefore, that the prior art required a motion device to lower the gripper toward the part to be picked up, an additional motion device to raise the gripper after the part had been secured and yet still further motion devices to effect translation from one location to another. In a pneumatically operated system, the motion device to raise the gripper from the presentation site requires secondary control and valving as well as sensors or timers to assure that the gripper is retracted only when the component part is secured thereto.